1. Field of the Invention
The present invention relates to a piezoelectric buzzer comprising a piezoelectric diaphragm which is preferably stored in a case, and more particularly, it relates to a piezoelectric buzzer having improved structures of metal terminals which are connected to the piezoelectric diaphragm and drawn out from the case.
2. Description of the Background Art
FIG. 1 is a sectional view showing an example of a conventional piezoelectric buzzer 1. The piezoelectric buzzer 1 has a case 2 which is made of synthetic resin, for example. This case 2 is provided with a case body 2a having an opening in its lower portion, and a back cover 2b which is fixed to the case body 2a for closing the opening in the lower portion.
The case 2 houses a piezoelectric diaphragm 3, which comprises a metal plate 3a and a piezoelectric vibrator 3b mounted to the lower surface of the plate 3a. The piezoelectric vibrator 3b is prepared by forming electrodes on both major surfaces of a piezoelectric ceramic plate. This piezoelectric diaphragm 3 is a unimorph piezoelectric vibrator.
A pair of metal terminals 4 and 5 are mounted on the back cover 2b. These metal terminals 4 and 5 have terminal drawing portions 4a and 5a which are drawn out from the case 2 through the back cover 2b, respectively. Further, the metal terminals 4 and 5 are bent at inner ends of the terminal drawing portions 4a and 5a along an inner surface of the back cover 2b, to define terminal fixing portions 4b and 5b, respectively. A pair of projections (not clearly shown in FIG. 1) are integrally provided with the back cover 2b on both sides of the terminal fixing portions 4b and 5b, respectively, and caulked for fixing the terminal fixing portions 4b and 5b, to the inner surface of the back cover 2b.
Inner ends of the terminal fixing portions 4b and 5b are upwardly bent so that connecting portions 4c and 5c are defined in forward ends of the upwardly bent portions. The connecting portion 4c is brought into contact with the electrode (not shown) which is formed on the lower surface of the piezoelectric vibrator 3b, to be thereby electrically connected to the piezoelectric vibrator 3b. The electrode provided on the upper surface of the piezoelectric vibrator 3b is electrically connected to the metal plate 3a, while the connecting portion 5c of the metal terminal 5 is brought into contact with the metal plate 3a so that the metal terminal 5 is electrically connected with the metal plate 3a.
Each of the metal terminals 4 and 5 may be replaced by a metal terminal 6 having a linearly extending terminal drawing portion 6a, which is bent on an upper end to define a connecting portion 6b, as shown in FIG. 2. In this metal terminal 6, the upper portion of the linearly extending terminal drawing portion 6a is embedded in the back cover 2b of the piezoelectric buzzer i shown in FIG. 1, to be thereby fixed to the back cover 2b. Further, the forward end of the connecting portion 6b is brought into contact with the piezoelectric vibrator 3b or the metal plate 3a.
However, it is impossible to provide a relatively larger area for fixing the metal terminal 6 to the inner surface of the back cover 2b. If the back cover 2b is deformed at the portion fixed with the metal terminal 6 due to heat application during soldering, therefore, the contact position or the contact pressure may be changed at the portion of the metal terminal 6 which is in contact with the piezoelectric diaphragm 3. Consequently, the characteristics of the piezoelectric buzzer 1 may disadvantageously be deteriorated.
This problem can be solved in the metal terminals 4 and 5 shown in FIG. 1, which are provided with the terminal fixing portions 4b and 5b along the inner surface of the back cover 2b. However, the metal terminals 4 and 5 are bent to be substantially U-shaped at the forward ends of the terminal fixing portions 4b and 5b thereby defining the connecting portions 4c and 5c, and hence it is necessary to sufficiently increase the distance between the inner surface of the back cover 2b and the piezoelectric diaphragm 3. Consequently, it is impossible to reduce the vertical length of the piezoelectric buzzer 1, and hence the the thickness of the buzzer 1 cannot be reduced.
Further, it is necessary to bend the metal terminals 4 and 5 at the forward ends of the terminal fixing portions 4b and 5b at considerable angles for reducing the relative angles between the contact portions 4c and 5c and the terminal fixing portions 4b and 5b. Consequently, work hardening is easily caused in the bent portions, to reduce spring properties of the metal terminals 4 and 5 in these portions.
Further, spring pressures caused by the bent portions may be increased to suppress vibration of the piezoelectric diaphragm 3, leading to deterioration of the characteristics. In order to solve this problem, the diameters of the metal terminals 4 and 5 may be reduced for lowering the spring pressures.
When the diameters are reduced, however, the metal terminals 4 and 5 are reduced in bending strength such that the terminals may be bent in undesirable directions in handling. In this case, it is difficult to arrange the metal terminals 4 and 5 to have desired shapes in the piezoelectric buzzer 1.